Lake Rotorua

A variety of streams feed the lake. Of these, the Hamurana Stream has the greatest flow. Geothermal inputs flow via streams such as the Puarenga and Waiohewa Streams, and there are hot springs along the lake’s southern shore. There are two monitoring sites for this lake located north and south of Mokoia Island. Each has a maximum depth of 20m. The lake’s aquatic plant remains low but stable. The invasive condition has improved slightly because Egeria declined in Lake Rotorua in the late 1980s and has never recovered. Future water quality improvements in this lake will cause aquatic pest plant species to proliferate, increasing the risk of large weed strandings. Lake Rotorua contains three of the region’s worst aquatic pest plant species and poses a risk to neighbouring lakes that are free of these species. Internal phosphorus and nitrogen recycling between the sediment and water column contributes a significant proportion of the nutrient load to Lake Rotorua. This, combined with the relatively old age of inflowing nutrient-laden groundwater, means restoration of the lake isn’t likely to be achieved quickly. Restoration work on Lake Rotorua continues to ensure the lake meets its long-term water quality (TLI) targets. A range of intervention techniques have been implemented, including alum dosing of two tributary streams as a short-term measure to reduce phosphorus levels, rules designed to reduce nitrogen inputs from the catchment and sewage reticulation to reduce septic tank inputs.